Conventional screw drive assemblies are known for driving collated screws in which screws are connected to each other by a retaining strip of plastic material. Screws carried by such strips are adapted to be successively advanced to a position in alignment with the bit of a reciprocating power screwdriver.
The invention represents a modification of prior art devices to provide a strip advance and release mechanism.
The prior art suffers from the disadvantage that a cover plate must be removed in order to access the screw strip when jamming occurs or if the strip is to be removed. Removal and replacing the cover plate involves significant time and working conditions may be such that handling small parts is difficult. Misplacing or loosing the plate or retaining screws renders the entire assembly inoperative and replacements may not be readily available. Therefore the invention addresses this disadvantage by providing a quick release mechanism to enable the strip to be easily withdrawn without requiring the cover plate to be removed.
When the lead screw of a strip is located and aligned, the power screwdriver bit may be used to screw the fastener into a work piece. In the course of the bit engaging the screw and driving it into the work piece, the lead screw becomes detached from the frangible plastic strip leaving the remainder of the strip as a continuous undisturbed length.
Such conventional strips are described for example in U.S. Pat. No. 4,167,229 issued Sep. 11, 1979 the disclosure of which is specifically incorporated herein by reference.
When such strips are used in a power screwdriver, the strip serves to continuously feed successive screws into a position where they may be automatically engaged by the screwdriver bit when properly aligned. The strip further serves in assisting to drive the screw into a work piece. In the strip, each screw has a threaded shaft which is threadably engaged in a sleeve of the plastic strip. Therefore when the screwdriver engages and rotates each screw, the screw turns within the sleeve thereby acting to guide the screw as it moves downwardly into threaded engagement with the work piece.
Preferably once the tip of the screw becomes engaged in the work piece, the head of the screw comes into contact with the sleeve and further downward movement of the screw into the work piece draws the head downwardly and ruptures the sleeve. The sleeve generally has a relatively solid back strap with frangible holding straps wrapping around the screw which break when the screw head passes through the sleeve. The remainder of the strip remains substantially intact as a continuous length after the lead screw has broken away from its frangible straps. Since the remainder of the strip is continuous and undisturbed, advancing the strip with each successive screw to be driven follows a repetitive cycle.
Conventional power screwdrivers for driving such collated strips are described in U.S. Pat. No. 4,146,071 to Mueller issued Mar. 27, 1976, and U.S. Pat. No. 5,186,085 to Monacelli issued Feb. 16, 1993. The disclosures of the above patents are specifically incorporated herein by reference.
Conventional power screwdrivers include a screwdriver shaft which is rotatably and reciprocally housed in the apparatus. The shaft is connected to a conventional pistol grip screwdriver and driven by the electric motor of the screwdriver. The downward portion of the shaft includes a screw driving bit which may be interchangeable, for engaging the head of each successive screw as the screw is moved into a locating driving position axially aligned under the screwdriver shaft.
The screw strip is fed through a lateral slot in the slide body. The advancing mechanism and screws may jam up within the lateral slot if there is any malfunction or foreign matter enters the lateral slot. Conventional screw driving assemblies have a lateral slot which is formed between a rear wall of the slide body and a forward removable cover plate. In order to remedy the jam situation or to remove an unused portion of a strip, it is necessary for the operator to remove a holding screw and the cover plate. On construction sites or in manufacturing environments it may be very inconvenient to handle small pieces such as the retaining screw and cover plate. If the operator accidentally drops these parts they may be irretrievably lost and cause considerable inconvenience since replacement parts are not readily available.
Therefore it is desirable to produce a screw driving assembly which includes means by which the screw strip can be removed from the lateral slot preferably without requiring disassembly of the screw driving apparatus.
Another disadvantage of prior art strip advance mechanisms, is that drive pawls which engage and advance the strip move along a path which is not parallel to the direction in which the strip is to be advanced. Such drive pawls cause some binding of the screws and screw strip which are being advanced and therefore require greater forces to be applied to the strip to advance it.